Processing data from a portable processing device

1. A computer-implemented method of controlling a portable processing device to switch the portable processing device from a lower-energy data generating state to a higher-energy data generating state, the method comprising:

processing data generated by the portable processing device in the lower-energy data generating state to determine whether the portable processing device has moved more than a threshold distance in a predetermined time; and

when it is determined that the portable processing device has moved more than the threshold distance in the predetermined time, switching the portable processing device to the higher-energy data generating state;

wherein processing data generated by the portable processing device in the lower-energy data generating state to determine whether the portable processing device has moved more than the threshold distance comprises:

(a) receiving data generated by the portable processing device defining a sequence of positions and, for each respective position, an accuracy of the position;

(b) for each of a plurality of positions in the sequence, processing the data defining the position and the accuracy of the position as well as the data defining a preceding position in the sequence and the accuracy of the preceding position, to determine whether the position is more than a first threshold distance from the preceding position; and

(c) processing data defining a time-ordered set of the positions for which it was determined that the position is more than the first threshold distance from the preceding position, to determine whether a distance between the position at the latest time in the time-ordered set and any position at an earlier time in the time-ordered set is greater than a second threshold distance;

wherein, when it is determined that the distance between the position at the latest time in the time-ordered set and any position at the earlier time in the time-ordered set is greater than the second threshold distance, the portable processing device is switched from the lower-energy data generating state to the higher-energy data generating state; and

wherein the processing to determine whether the position is more than the first threshold distance from the preceding position comprises:

(a) calculating a position difference between the position and the preceding position;

(b) calculating an accuracy difference between the accuracy of the position and the accuracy of the preceding position; and

(c) comparing the position difference and the accuracy difference to determine whether the position is more than the first threshold distance from the preceding position, wherein the processing to determine whether the position is more than the first threshold distance from the preceding position comprises determining whether:

| x 2 −x 1 |>( a 2 −a 1 ) k

 where x 2 is the position, x 1 is the preceding position, a 2 is the accuracy of the position, a 1 is the accuracy of the preceding position, and k is a constant, and a 2 and a 1 comprising values that decrease as the accuracy increases.

2. A non-transitory computer readable medium comprising computer program instructions configured to program a processor to perform the method of claim 1 .

3. A method according to claim 1 , wherein the first threshold distance is a function of the accuracy of the position and the accuracy of the preceding position.

4. A computer-implemented method of processing data from a portable processing device to determine when the portable processing device has begun a journey, the method comprising:

receiving data generated by the portable processing device defining a sequence of positions and, for each respective position, an accuracy of the position;

for each of a plurality of positions in the sequence, processing the data defining the position and the accuracy of the position as well as the data defining a preceding position in the sequence and the accuracy of the preceding position, to determine whether the position is more than a first threshold distance from the preceding position;

processing data defining a time-ordered set of the positions for which it was determined that the position is more than the first threshold distance from the preceding position, to determine whether a distance between the position at the latest time in the time-ordered set and any position at an earlier time in the time-ordered set is greater than a second threshold distance; and

when it is determined that the distance between the position at the latest time in the time-ordered set and any position at the earlier time in the time-ordered set is greater than the second threshold distance, it is determined that the portable processing device has begun a journey;

wherein the processing to determine whether the position is more than the first threshold distance from the preceding position comprises:

(a) calculating a position difference between the position and the preceding position;

(b) calculating an accuracy difference between the accuracy of the position and the accuracy of the preceding position; and

(c) comparing the position difference and the accuracy difference to determine whether the position is more than the first threshold distance from the preceding position, wherein the processing to determine whether the position is more than the first threshold distance from the preceding position comprises determining whether:

| x 2 −x 1 |>( a 2 −a 1 ) k

 where x 2 is the position, x 1 is the preceding position, a 2 is the accuracy of the position, a 1 is the accuracy of the preceding position, and k is a constant, and a 2 and a 1 comprising values that decrease as the accuracy increases.

5. A non-transitory computer readable medium comprising computer program instructions configured to program a processor to perform the method of claim 4 .

6. A method according to claim 4 , wherein the first threshold distance is a function of the accuracy of the position and the accuracy of the preceding position.

7. A computer-implemented method of processing data from a portable processing device to determine when the portable processing device has ended a journey, the method comprising:

receiving data generated by the portable processing device defining a sequence of positions and, for each respective position, an accuracy of the position;

for each of a plurality of positions in the sequence, processing the data defining the position and the accuracy of the position as well as the data defining a preceding position in the sequence and the accuracy of the preceding position, to determine whether the position is more than a first threshold distance from the preceding position;

for the positions for which it is determined that the position is more than the first threshold distance from the preceding position in the sequence, generating a time-ordered set of positions;

processing data defining the time-ordered set of positions to determine whether a distance between the position at the latest time in the time-ordered set and any position at an earlier time in the time-ordered set is greater than a second threshold distance; and

when it is determined that the distance between the position at the latest time in the time-ordered set and each position at the earlier time in the time-ordered set is not greater than the second threshold distance, it is determined that the portable processing device has ended a journey;

wherein the processing to determine whether the position is more than the first threshold distance from the preceding position comprises:

(a) calculating a position difference between the position and the preceding position;

(b) calculating an accuracy difference between the accuracy of the position and the accuracy of the preceding position; and

(c) comparing the position difference and the accuracy difference to determine whether the position is more than the first threshold distance from the preceding position, wherein the processing to determine whether the position is more than first threshold distance from the preceding position comprises determining whether:

| x 2 −x 1 |>( a 2 −a 1 ) k

 where x 2 is the position, x 1 is the preceding position, a 2 is the accuracy of the position, a 1 is the accuracy of the preceding position, and k is a constant, and a 2 and a 1 comprising values that decrease as the accuracy increases.

8. A method according to claim 7 , wherein the processing to determine whether the position is more than the first threshold distance from the preceding position further comprises:

calculating a calculated speed of the portable processing device travelling from the preceding position to the position; and determining whether the calculated speed is less than a threshold speed.

9. A method according to claim 7 , wherein the processing to determine whether the position is more than the first threshold distance from the preceding position further comprises:

calculating a calculated acceleration of the portable processing device travelling from the preceding position to the position; and

determining whether the calculated acceleration is less than a threshold acceleration.

10. A method according to claim 7 , wherein the time-ordered set of positions is generated by:

processing each position for which it is determined that the position is more than the first threshold distance from the preceding position in the sequence, to:

(a) calculate a projected position in dependence upon the preceding position and a speed at the preceding position defined by data generated by the portable processing device; and

(b) calculate a filtered position by combining the projected position and the position in dependence upon the accuracy of the preceding position and the accuracy of the position; and

generating a time-ordered set of the filtered positions.

11. A non-transitory computer readable medium comprising computer program instructions configured to program a processor to perform the method of claim 7 .

12. A method according to claim 7 , wherein the first threshold distance is a function of the accuracy of the position and the accuracy of the preceding position.